Employers are not allowed to be ageist these days - I am surprised that your application forms ask for age or DoB as age discrimination is not allowed, I don't have it on my c.v. any more. I work in the NHS and many of us are over 60, as you say our experience and expertise is valued.
Make sure that your c.v. and forms reflect your state of health and that you are not expecting to retire soon or have many absences.
Unfortunately in the current financial climate the NHS in England is not recruiting at the moment otherwise I would point you in that direction, but general practice will be the way forward in the latest reorganisation. I can only suggest that you either watch the press, or look on NHSJobs website as GPs advertise posts there, or mailshot your local surgeries speculatively in case they are succession planning.
I wish you good luck - let us know how you get on.
PS our local PO has just taken on new counter assistants who have had to be retrained for the role - always worth asking there as well. Don't forget that companies like B&Q have a policy of taking on older people because of their experience and life skills - try there too. Re the supermarket, do bear in mind local issues - we had a supermarket open over the road and they had 2000 applicants for 50 posts, so could be very choosy.